Vibration control system and improvements in or relating to skis

ABSTRACT

Vibration control systems are described which provide for the variation in stiffness and damping in a structure. The systems are based on the use of rheological fluid, with examples provided of magnetorheological fluid flex actuators and semi-active damping systems. An adaptive vibration control system is also described incorporating sensors, a signal processor and a power supply together with the fluid flex actuators and semi-active damping systems. Embodiments are described for use in and with skis.

The present invention relates to vibration control systems and inparticular, though not exclusively, to an adaptive control system tovary flex and damping in skis during use.

It is known that vibration of an object can be suppressed in objectsmanufactured with a calculated stiffness and damping. However, when theobject is subjected to a range of operating conditions the frequency ofvibration can vary i.e. the bandwidth increases. Objects having a fixedstiffness and damping cannot suppress vibration at varying frequenciesand as a result the object is prone to vibration with deleteriouseffect.

An area where vibration reduces performance is in skiing. Vibrationcauses a ski to ‘chatter’ and so loose edge contact. Manufacturers haveengineered skis by varying geometry, materials and constructiontechniques in an effort to suppress vibration, but such skis tend to belimited to use in certain environments. For example, male downhill raceskiers use skis which have a high stiffness whereas recreational skiershave more flexible skis. It is recognised that it would be advantageousto provide a ski in which the stiffness and damping could be variedduring use and so improve the handling of a ski in a range ofenvironments.

It is an object of at least one embodiment of the present invention toprovide a vibration control system which includes active flex control tovary the stiffness of an object during use.

It is a further object of at least one embodiment of the presentinvention to provide a vibration control system which includes asemi-active damping system to change the damping level so as tooptimally counteract motion with a controlled resistive motion.

It is a yet further object of at least one embodiment of the presentinvention to provide a vibration control system which automaticallyadapts to surrounding conditions to provide active vibration control.

It is an object of at least one embodiment of the present invention toprovide a ski including active flex control.

It is a further object of at least one embodiment of the presentinvention to provide a ski including a semi-active damping system.

It is a yet further object of at least one embodiment of the presentinvention to provide a ski having automatic adaptive control ofstiffness and damping during use.

According to a first aspect of the present invention there is provided avibration control system, the system comprising a structure including achamber and a means for creating a variable applied field within thechamber, wherein the chamber is substantially filled with a rheologicalfluid which under the influence of the applied field causes a variationin the stiffness of the structure.

The rheological fluid may be an electrorheological fluid which undergoesa change in viscosity proportional to a change in electric field.Advantageously the rheological fluid is a magnetorheological fluid whichundergoes a change in viscosity proportional to a change in appliedmagnetic field.

Preferably the applied field is a continuously variable applied field.

Preferably, the means for creating a variable applied field comprises anelectromagnetic coil. A variable power source may be applied to thecoil.

The structure may include a first member having a first surface and asecond member having a second surface, the surfaces being inner walls ofthe chamber and are arranged to face each other, wherein the rheologicalfluid is located therebetween such that in the presence of the appliedfield, a shear force is set-up between the surfaces by virtue of thefluid which varies the stiffness of the structure.

Alternatively, the structure may include a piston moveable within thechamber. Preferably the piston is an electromagnet such that themagnetic field strength may be varied within the chamber. Morepreferably, the piston is hollow providing a fluid flow paththerethrough. Thus as the magnetic field strength is increased, thefluid particles in the piston align. This results in an apparentincrease in viscosity that reduces the ability of the fluid to flowthrough the piston. Therefore by increasing the magnetic field,resistance to flow reduces the flex and hence increases the stiffness ofthe structure. The converse is also true. This vibration control systemmay be referred to as a resistive flow active flex system.

According to a second aspect of the present invention there is provideda vibration control system, the system comprises a mounting surface uponwhich is located a flexible hose, the hose having a firstcross-sectional area filled with a rheological fluid and ends abutted tothe surface.

The system provides semi-active damping as any flexing of the mountingsurface will create a change in the cross-sectional area of the hose andcause the hose to act as a pump, while application of an applied fieldwill cause the fluid to act as a valve. Consequently, an increase infield increases the fluid viscosity, the valve makes it more difficultto pump the fluid and thus more force is required to flex the hose,providing a damping effect.

The rheological fluid may be an electrorheological fluid which undergoesa change in viscosity proportional to a change in electric field.Advantageously the rheological fluid is a magnetorheological fluid whichundergoes a change in viscosity proportional to a change in appliedmagnetic field.

Preferably the rheological fluid is ‘Rheonetic Fluid’ as produced byLord Corporation, USA.

Preferably a plurality of hoses are located on the surface. Morepreferably the hoses are located symmetrically on the surface.

According to a third aspect of the present invention there is providedan adaptive vibration control system, the system comprising sensingmeans to determine one or more environmental characteristics, a signalprocessor to determine a controlling response to the characteristics andvibration control means responsive to the controlling response tocounter vibration.

Preferably the sensing means is at least one sensor. More preferably thesensing means is a multi-sensor array. Advantageously the sensor arrayis a distributed array of PVDF piezo-sensors.

Preferably the signal processor identifies characteristic vibrationpatterns from the sensors. The signal processor may also include acontrol algorithm to identify the patterns. Preferably also the signalprocessor includes a feedback loop from the vibration control means toregulate the response.

Advantageously, the signal processor is a microprocessor. Morepreferably, the microprocessor is a proportional-differential-integralprocessor. Advantageously, the control algorithm is a fuzzy logiccontrol algorithm to provide an intelligent control unit. Such anintelligent control unit with a fuzzy logic control algorithm programmedinto the microprocessor may grade the vibration being monitored andcontrol a graded response from the vibration control means.

Preferably the vibration control means comprises a vibration controlsystem according to the first aspect. Preferably also the vibrationcontrol means comprises a vibration control system according to thesecond aspect. Advantageously the controlling response will determinethe applied field.

Alternatively, the vibration control means comprises the vibrationcontrol system of the first aspect in combination with a direct shearmode semi-active damping system.

The direct shear mode semi-active damping system may comprise a fluidfilled chamber which is acted upon by a piston to vary thecharacteristics of the fluid. More preferably, the fluid is amagneto-rheological fluid.

Advantageously, the piston is an electromagnet having a variablemagnetic field strength. Thus in use, movement of the piston varies themagnetic field strength which in turn influences the alignment of ironparticles in the fluid, the aligned particles being sheared as thepiston moves.

Advantageously the adaptive vibration control system may be automatic.Alternatively the adaptive vibration control system may operate from aswitch.

Preferably also the adaptive vibration control system includes a powersupply located adjacent the system. More preferably the power supply isdriven from vibration experienced by the structure. The power supply mayinclude piezo material such that movement of the structure creates anelectric signal.

Further, the adaptive vibration control system may include a userinterface. The user interface may allow a user to provide the signalprocessor with data on one or more environmental characteristics. Theuser interface may comprise a wire or wireless connection to a remotedevice. The remote device may be a handheld device. More preferably, theremote device is a mobile PDA/phone.

According to a fourth aspect of the present invention there is provideda ski, the ski including a vibration control system according to thefirst aspect to vary stiffness in the ski.

Preferably the vibration control system is arranged fore and aft on theski body. Advantageously the vibration control system is arrangedlongitudinally on the ski, on either side of a binding.

According to a fifth aspect of the present invention there is provided aski, the ski including a vibration control system according to thesecond aspect to vary damping in the ski.

Preferably the vibration control system is arranged fore and aft on theski body.

According to a sixth aspect of the present invention there is provided aski, the ski including a vibration control system according to the firstand second aspects to vary both stiffness and damping in the ski.

Preferably the vibration control systems are arranged fore and aft onthe ski body. Advantageously the vibration control system according tothe first aspect is arranged longitudinally on the ski, on either sideof a binding.

According to a seventh aspect of the present invention there is provideda ski, the ski including an adaptive vibration control system accordingto the third aspect to provide adaptive control of vibration in the ski.

Preferably the sensor arrays are positioned at modal points on the ski.More preferably the sensor arrays are located at a fore and aft locationin a body of the ski.

Preferably also the vibration control means are located a modal pointson the ski. More preferably the vibration control means are located atfore and aft locations on a body of the ski. Advantageously thevibration control means according to the first aspect is arrangedlongitudinally on the ski, on either side of a binding.

Preferably the power supply powers the microprocessor and the variablemagnetic field. More preferably the power supply comprises a layeredpiezo-ceramic. The piezo-ceramic may be located on the ski at a positionwhere a skier's boot will rest. Thus the layered piezo-ceramic isconfigured at the point of maximum weight concentration to ensure itflexes as the skier moves. In this embodiment, power generation comesfrom the skier's movement over the ski, rather than the vibrating ski.

According to an eighth aspect of the present invention there is provideda chassis for mounting on a ski, the chassis including a vibrationcontrol system to control vibration of the ski in use.

By mounting the vibration control system on a chassis, the ski geometrycan be varied as required.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the following drawings in which:

FIG. 1 is a schematic diagram of a ski according to an embodiment of thepresent invention;

FIG. 2 to is an exploded view of a portion of FIG. 1 illustrating avibration control system for varying stiffness according to anembodiment of the present invention;

FIG. 3(a) is an illustration of an alternative embodiment of a vibrationcontrol system for varying stiffness and FIG. 3(b) shows this embodimentmounted on a ski;

FIG. 4 is an exploded view of a portion of FIG. 1 illustrating avibration control system for varying damping according to an embodimentof the present invention;

FIG. 5(a) is an illustration of an alternative embodiment of a vibrationcontrol system for varying damping and FIG. 5(b) shows this embodimentmounted on a ski;

FIG. 6 is a schematic diagram of an adaptive vibration control systemaccording to an embodiment of the present invention;

FIGS. 7(a) and 7(b) are illustrations of an adaptive vibration controlsystem mounted on a ski, according to an embodiment of the presentinvention;

FIGS. 8(a) and (b) are illustrations of a power supply for use on a skiaccording to an embodiment of the present invention; and

FIGS. 9(a) and (b) are schematic diagrams of a ski chassis, according toan embodiment of the present invention, mounted on a ski.

Reference is initially made to FIG. 1 of the drawings which depicts aski, generally indicated by reference numeral 10, according to anembodiment of the present invention. Ski 10 has a conventional compositestructure 12 providing a tip 14, tail 16, upper surface 18 and edges 20a,b. Mounted upon the upper surface 18, towards the edges 20 a,b arefour symmetrically positioned damping support bars 24 a,b. The bindings(not shown) will be attached to the ski at the support bars 24 a,b. Thisposition will therefore bear the weight of the skier. Over the dampingbars 22 and the support bars 24 are control rails 26 a,b. The bars 22,24and rails 26 are all arranged longitudinally on the ski 10.

Between the damping bars 22 and the control rails 26 is located arheological fluid 28. Rheological fluids are well known and operate byincreasing the viscosity of the fluid in response to an applied field.In the embodiment shown the fluid 28 is a magnetorheological fluid whichundergoes a change in viscosity in response to a changing magneticfield. This arrangement of bars 22, rails 26 and fluid 28 provides avibration control system in the form of an active flex control which canvary stiffness in the ski 10.

A first embodiment of the flex control system is illustrated with theaid of FIG. 2. FIG. 2 shows the interface between the damping bars 22and the control rails 26. A magnetic field is applied between the bars22 and rails 26 in the direction of arrow A. The magnetic field isapplied via coils 30 (only one shown in FIG. 1) mounted on the rails 26.The consequent increase in viscosity of fluid 28 creates a shear forcein direction BB′. The control rails 26 mechanically amplify thedirect-shear mode and thus control the stiffness matrix (the inverse ofside flex) of the composite 12 making up the ski 10. The direct-shearmode when applied reduces the movement of the bars 22 with respect tothe rails 26. Vibration is thus controlled as the resultant change instiffness alters the deflection of the ski 10 in response to impulses.Control can be varied by varying the amount of fluid 28 and the appliedfield. Thus at a high magnetic field the bars 22,24 and rails 26 willeffectively ‘lock’ providing the ski 10 with a high stiffness. Thearrangement shown in FIG. 2 provides active flex control to the ski 10when the magnetic field is applied. The field is switched on via aswitch 32 located on the upper surface 18 of the ski 10 or via anadaptive vibration control system, described hereinafter with referenceto FIG. 6.

In the preferred embodiment small volumes of fluid 28 are used whichrequire small field strengths so that the ski 10 can be both lightweightand cheap to produce.

An alternative embodiment of the active flex control is shown in FIG. 3.In this arrangement actuators, generally indicated by reference numeral50, provide the active flex control by a resistive flow concept. Eachactuator 50, comprises a chamber 52 which is filled with amagnetorheological fluid 54. Within the chamber 52 is arranged anelectromagnetic coil 56, in which passes a piston or slider head 58. Thepiston 58 includes a plastic sleeve 60, acting as a plunger. Further thepiston has a hollow bore (not shown). In use the steel piston head 58acts as an electromagnet and varies the magnetic field strength withinthe fluid filled chamber 52. Fluid 54 flows through the hollow bore. Asthe magnetic field strength is increased, the fluid particles in thepiston align in the direction shown by broken line C by virtue of themagnetic flux path shown by arrow D. This results in an apparentincrease in viscosity that reduces the ability of the fluid 54 to passthrough the piston 58. Therefore, by increasing the magnetic field,resistance to flow reduces the flex, and hence increases the stiffness,of the ski to which the actuator is attached. The stiffness can bedecreased by decreasing the magnetic field strength also. As the skiflexes, resistive flow reduces displacement of the piston sleeve 60.

FIG. 3(b) illustrates four active flex actuators 53 a-d, located on aski 62. The actuators are longitudinally arranged on the ski, in pairs,symmetrically about the binding position 64.

As the ski 10, 62 can vary its stiffness as described hereinbefore,conventional passive-damping techniques would be insufficient as thedamping requirements will need to vary. Ski 10 incorporates asemi-active damping system, best illustrated in FIG. 4, to change thedamping level and optimally counteract motion with a controlledresistive motion. This is achieved by applying the pressure driven flowmode of operation for controllable fluids.

Reference is now made to FIG. 4 of the drawings which illustrates adamping bar 22 as a vibration control system according to an embodimentof the present invention. The damping bar 22 has ends 34 a,b which abutthe upper surface 18 of the ski 10. Each bar 22 is made of a flexiblehose. The hose is filled with fluid 28. The fluid 28 is sealed in thehose. When mounted on the ski 10, the hose has a uniform cross-section.The hose acts as a pump when flexed. Flexing creates a change in thecross-sectional area and the resulting restriction produces a pressurechange which drives the fluid 28. When the magnetic field, describedhereinbefore, is applied the viscosity of the fluid 28 increases. Thefluid then acts like a valve making it more difficult to pump the fluidand therefore requiring more force to flex the hose. This dampingarrangement of fluid filled hoses or fibres can be arranged along thelength of the ski 10 to act against vibration.

Like the active flex control, the semi-active damping system can beconstructed using small amounts of fluid 28 placed in fibres to reduceweight and cost of the ski 10.

A further embodiment of a semi-active damping system is shown in FIG. 5.The system comprises a damper, generally indicated by reference numeral70, which acts in the direct shear mode of magnetorheological fluid toachieve semi-active damping. Damper 70 comprises magnetorheologicalfluid 72 filled chamber 74. A piston 76 is arranged within the chamberonto which is located an electromagnetic coil 78. The piston 76 thusacts as an electromagnet. The piston has a plastic sleeve 80 and isarranged within a steel sleeve 82. In use, vibration causes the plasticsleeve 80, to act as a plunger and force the piston 76 to move insidethe sleeve 82. This increases the magnetic field strength in themagnetic flux path E and causes iron particles in the fluid 72 to align,F, between the ends 84,86 of the piston 76 and the steel sleeve 82. Thealigned particles are sheared as the piston 76 moves. As the magneticfield increases the damping is increased.

Reference is now made to FIG. 5(b) which illustrates the dampers 70mounted on a ski 90, in pairs. Fore-body damping occurs at a position 92near the tip of the ski 90 while aft-body damping occurs at a position94 towards the tail of the ski. Positions 92 and 94 are selected to bethose regions of significant vibration on the ski when in use.

It will be appreciated by those skilled in the art that the active flexsystems and the semi-active damping systems described hereinbefore canbe used independently on a ski.

Reference is now made to FIG. 6 of the drawings which illustrates anautomatic adaptive vibration control system for ski 10,62,90. Amulti-sensor array 36 is located on a ski. The array 36 is made up of adistributed array of PVDF piezo-sensors. Though only one location forthe array 36 is shown in FIG. 1 for ski 10, it will be appreciated thatthe sensors could be located across the entire structure of a ski 10. Ina preferred embodiment the sensors are concentrated about regions ofsignificant vibration i.e. modal points on the ski. The typical modalpoints are located in the fore and aft body structure of the ski, seeFIG. 7(b) to be described hereinafter.

Signals from the sensors in the array 36 are input to a signalprocessing unit 38 which, using a stored algorithm, identifies acharacteristic vibration pattern dependent on the environmentalconditions and the handling of the ski 10. Unit 38 then determines aresponse proportional to the amplitude of the vibration which istransmitted to the coils 30 controlling the magnetic field strength.Thus the stiffness and damping can be controlled as describedhereinbefore. A feedback loop 40 is also provided to enable the amountof actuator response to be regulated.

Reference is now made to FIG. 7 of the drawings which illustrates a ski,generally indicated by reference numeral 100, including an adaptivevibration control system to provide active flex control and semi-activedamping, according to an embodiment of the present invention. Ski 100includes a matrix structure into which is arranged a pattern of adaptiveflex actuators 110 a-d and semi-active dampers 120 a-d. This may betermed a smart material 130. The smart material 130 is arrangedlongitudinally on the ski 100. At a point near the tip 112 is located afore-body control point (FCP) 114 and at a point near the tail 116 islocated an aft-body control point (ACP) 118.

Further on the ski 100 are arranged arrays of vibration sensors 140 a-e.These sensors 140 a-e are PVDF piezo-sensors which convert vibrationalmovement to an electrical signal indicative of the amount of vibrationexperienced. These sensors 140 a-e are positioned at positions, or modalpoints, where significant vibration is experienced by the ski 100. Thusthey are located fore and aft on the ski towards each side.

Located centrally on the ski 100, at the position of the binding is anintelligent control unit 150. Control unit 150 is an advanced version ofthe adaptive control unit illustrated in FIG. 6. The unit includes aproportional-differential-integral (PID) microprocessor 152 on amicrochip as the signal processor. A fuzzy logic control algorithm isprogrammed into the microprocessor 152, to grade the vibration beingmonitored by sensors 140 and control a graded response from the controls110,120. This ensures the system operates within bandwidths of vibrationand does not become unstable.

Also included with the intelligent control unit 150 is a control panel152 which allows a user to input values representative of environmentalcharacteristics into the microprocessor 152. For instance these may bethe skiers weight, style, ability and snow condition. The control panel152 may also include a main switch to enable and disable the unit 150.It will be understood that the control panel 152 may be remote from theunit 150. A cable to a switch located with the skier may, for example,be used. Alternatively the control panel may be a mobile telephone or aPDA (Personal Digital Assistant), providing the user with a wirelessconnection to the unit 150.

FIG. 6 also shows a power supply 42 used to drive the stiffness anddamping vibration control systems. A similar power supply will beincorporated in the intelligent control unit 150 also. In theembodiments described hereinbefore this supply 40 would be the coils.Alternatively electromagnets could be used. The power supply 42 couldalso be replaced by a system such as piezoelectrics which are poweredfrom the movement of the skis. FIG. 8 illustrates such a powergeneration system.

Referring initially to FIG. 8(a), mounted on a ski 160, at a pointbetween the binding toe and heel piece, is a layered piezo-ceramic (PZT)162. The layers 164,166,168 are parallel to an upper surface 170 of theski 160 as illustrated in FIG. 8(b). Between the PZT 162 and the surface170 is a raised section 172. The raised section 172 provides a smallcontact area with the PZT 162 compared to a large contact area on theski 160. In use, a skiers weight is concentrated on the ski at the pointshown by arrow G. This is directly on the PZT 162 and provides a pointloading to increase strain through the layers of the PZT 162 to increasethe output from the PZT 162 as the power supply 40. Thus the power isgenerated by the skiers movement on the ski.

A further embodiment of the present invention is shown in FIG. 9. FIG. 9illustrates a ski chassis, generally indicated by reference numeral 180,which includes an adaptive vibration control system according to thepresent invention. The chassis 180 can be mounted on a ski 182 at thebinding 184. Indeed the binding 184 may be mounted upon the chassis 180via a binding mount provided as part of the chassis 180. The chassiscomprises flex actuators 186,188 located at either side of the bindingmount 184, semi-active dampers 190,192 at modal points towards the endsof the chassis, a power supply mounted centrally with the control unit.These components are all as described hereinbefore with reference toFIG. 1 to 8. By locating the components on a chassis, this raisedsuperstructure moves the rheological fluid away from the ski's neutralaxis and thus mechanically amplifies any change occurring in the controlelements. A further advantage to using a chassis is that it raises thebinding off the ski and increases the swing weight or torque to put theski onto its edge. This is regulated in competition and also has healthimplications in terms of knee damage. In using a chassis this can bedesigned to conform with regulations. A yet further advantage ofincorporating a vibration control system on a chassis is that a singlechassis can be interchanged between skis of varying geometry asrequired.

The principal advantage of the present invention is that it provides avibration control system which, when incorporated into a ski, allowscontrol of vibration and improves handling and skier performance byadapting physical properties of the ski.

A further advantage of the present invention is that it allows a singleski to be used for a variety of environmental conditions by varying thestiffness of the ski.

A yet further advantage of the present invention is that it provides asimple pump for semi-active damping control through use of a fluidfilled flexed hose.

It will be appreciated by those skilled in the art that variousmodifications may be made to the invention hereindescribed withoutdeparting from the scope thereof. For example, while the embodimentshown is a ski, any object subjected to vibration over a wide bandwidthcould be fitted with the vibration control system of the presentinvention. Additionally, the number of damping bars and shear-modeinterfaces could be varied on an object.

1-39. (canceled)
 40. A vibration control system, the system comprising amounting surface upon which is located a flexible hose, the hose havinga first cross-sectional area filled with a rheological fluid and endsabutted to the surface.
 41. A vibration control system as claimed inclaim 40, wherein the rheological fluid is an electrorheological fluidwhich undergoes a change in viscosity proportional to a change inelectric field.
 42. A vibration control system as claimed in claim 40,wherein the rheological fluid is a magnetorheological fluid whichundergoes a change in viscosity proportional to a change in appliedmagnetic field.
 43. A vibration control system as claimed in claim 40,wherein a plurality of hoses are located on the surface.
 44. A vibrationcontrol system as claimed in claim 43, wherein the hoses are locatedsymmetrically on the surface.
 45. An adaptive vibration control system,the system comprising sensing means to determine one or moreenvironmental characteristics, a signal processor to determine acontrolling response to the characteristics and vibration control meansresponsive to the controlling response to counter vibration.
 46. Anadaptive vibration control system as claimed in claim 45, wherein thevibration control means comprises a structure including a chamber and ameans for creating a variable applied field within the chamber, whereinthe chamber is substantially filled with a theological fluid which underthe influence of the applied field causes a variation in the stiffnessof the structure.
 47. An adaptive vibration control system as claimed inclaim 45, wherein the vibration control means comprises a mountingsurface upon which is located a flexible hose, the hose having a firstcross-sectional area filled with a rheological fluid and ends abutted tothe surface.
 48. An adaptive vibration control system as claimed inclaim 45, wherein the sensing means is at least one sensor.
 49. Anadaptive vibration control system as claimed in claim 45, wherein thesensing means is a multi-sensor array.
 50. An adaptive vibration controlsystem as claimed in claim 45, wherein the multi-sensor array is adistributed array of PVDF piezo-sensors.
 51. An adaptive vibrationcontrol system as claimed in claim 45, wherein the adaptive vibrationcontrol system includes a power supply located adjacent the system, thepower supply including a piezo material such that movement of thematerial creates an electric signal.
 52. A ski, the ski including avibration control system, the system comprising sensing means todetermine one or more environmental characteristics, a signal processorto determine a controlling response to the characteristics and vibrationcontrol means responsive to the controlling response to countervibration.
 53. A ski as claimed in claim 52, wherein the vibrationcontrol means comprises a structure including a chamber and a means forcreating a variable applied field within the chamber, wherein thechamber is substantially filled with a theological fluid which under theinfluence of the applied field causes a variation in the stiffness ofthe ski.
 54. A ski as claimed in claim 52, wherein the vibration controlmeans comprises a mounting surface upon which is located a flexiblehose, the hose having a first cross-sectional area filled with atheological fluid and ends abutted to the surface.
 55. A ski as claimedin claim 52, wherein the vibration control system comprises vibrationcontrol means comprising a structure including a chamber and a means forcreating a variable applied field within the chamber, wherein thechamber is substantially filled with a theological fluid which under theinfluence of the applied field causes a variation in the stiffness ofthe ski, and vibration control means comprising a mounting surface uponwhich is located a flexible hose, the hose having a firstcross-sectional area filled with a theological fluid and ends abutted tothe surface to vary damping of the ski.
 56. A ski as claimed in claim52, wherein the sensing means is a multi-sensor array being adistributed array of PVDF piezo-sensors.
 57. A ski as claimed in claim52, wherein the sensing means is sensor arrays positioned at modalpoints on the ski.
 58. A ski as claimed in claim 52, wherein thevibration control means are located a modal points on the ski.
 59. A skias claimed in claim 52, further comprising a power supply comprising alayered piezo-ceramic, and wherein power generation comes from a skier'smovement over the ski acting on the piezo-ceramic.